Process for control of lubricants in an aluminium rolling mill

ABSTRACT

In the operation of an aluminum rolling mill, in which the lubricant is an oil-in-water emulsion, having an oil phase consisting of a hydrocarbon oil base, containing a free fatty acid and an amino-soap, the average particle size of the oil phase particles is periodically adjusted by the addition to the water phase either of multivalent metallic ion to increase particle size or of an alkali metal soap or material to generate an alkali metal soap by reaction with free fatty acid to reduce particle size so as to retain the particle size within an optimum range.

United States Patent [191 Tripathi PROCESS FOR CONTROL OF LUBRICANTS IN AN ALUMINIUM ROLLING NULL [75] Inventor: Krishna Chandra Tripathi,

Deddington, England [73] Assignee: Alcan Research and Development Limited, Montreal, Quebec, Canada [22] Filed: Jan. 12, 1972 [21] Appl. No.: 217,248

[30] Foreign Application Priority Data OTHER PUBLICATIONS Becher, Emulsions: Theory & Practice," 2nd Edn.,

(1965), pages 237; 238; 248 and 249.

Kirk-Othmer, Encycl. of Chem. TechnoL, Vol. 8, (1965), Pages 123; 125; 151 and 152.

Primary Examiner-W. Cannon Attorney-Robert S. Dunham et al.

[5 7] ABSTRACT In the operation of an aluminum rolling mill, in which the lubricant is an oil-in-water emulsion, having an oil phase consisting of a hydrocarbon oil base, containing a free fatty acid and an amino-soap, the average particle size of the oil phase particles is periodically adjusted by the addition to the water phase either of multivalent metallic ion to increase particle size or of an alkali metal soap or material to generate an alkalimetal soap by reaction with free fatty acid to reduce particle size so as to retain the particle size within an optimum range.

3 Claims, No Drawings PROCESS FOR CONTROL OF LUBRICANTS IN AN ALUMINIUM ROLLING MILL The present invention relates to the operation of rolling mills for rolling aluminium (which expression also includes aluminium alloys) and in particular to the lubrication of the aluminium during the rolling process.

It is well known in rolling aluminium to employ a rolling lubricant in the form of an oil-in-water emulsion, in which the oil phase comprises a light mineral oil having a substantial porportion of a fatty acid dissolved therein, the emulsion being stabilised by the use of an amine or amide soap.

It is common experience when using lubricants of this type that the surface finish of the rolled product gradually improves during a period of several days after a fresh charge of lubricant emulsion has been introduced into the mill and after a further period of time the results obtained fall away quite rapidly. It is an object of the present invention to overcome these difficulties.

Examination of the lubricant at various stages during the service life of a charge of lubricant in the lubrication system of a hot rolling mill has now revealed that the change in behaviour of the lubricant during its service life is due to changes in the average particle size. Whilst the optimum particle size of the dispersed oil phase is not the same for all oil-in-water lubricant emulsions of the present type, it appears to be true that for a particular lubricant there is an optimum range of particle size, which can be determined by experiment.

The practical experience with commercially available oil-in-water lubricant emulsions referred to above seems to result from the fact that the particle size of the freshly made-upemulsions is too small to provide the most satisfactory results. These oil-in-water emulsions serve as both lubricant and coolant. To serve as a good lubricant, an emulsion should wet the steel roll-surface well in order that the oil separating on the rolls as-the result of evaporation of water is distributed uniformly on the roll surface for the reduction of friction between the roll and the metal subjected to deformation. Furthermore the lubricant emulsion should prevent excessive metal or oxide transfer from the deformed metal surface to the rolls or vice versa. It is this characteristic of the rolling lubricant which seems to be dependent upon the particle size of the dispersed oil phase. Thus it has been found that for a particular oil-in-water lubricant composition a very small oil-phase particle size can result in very heavy pick-up of aluminium on the mill rolls, which results in the production of rolled aluminium of poor surface quality.

With oil-in-water lubricant compositions of the present type the oil phase comprises a light lcerosinic base oil, in which is dissolved a fatty acid as a load bearing additive and an amine-type soap as a stabiliser for the aqueous emulsion. The amine-type soap is usually a soap formed from an ethan'olamine, which is reacted with some of the fatty acid. It is usual to incorporate other substances, such as tricresyl phosphate, as extreme pressure and anti-wear additive and also surface active agents for spreading the lubricant on the roll surface. It has been found that the particle size at which optimum results are obtained is dependent upon both fatty acid content and the surface active agent content of the oil phase. It is found preferable to employ an oilin-water emulsion composition which will give optimum results at a particle size such that oil particles are not removed by filters of a fineness necessary to re move oxide particles, since this enables the removal of fine solid particles to be effected without at the same time loss of excessive quantities of oil in the filters.

It is an object of the present invention to provide a method of adjusting the particle size of a lubricant oilin-water emulsion, of which the oil phase contains a significant proportion of a fatty acid and an amino-soap, to any desired level and thereafter maintaining the particle size at this level. In referring to an amino-soap it is intended to refer to any soap in which the cation includes an -amine,-imine, -amide or -imide group, including ammonium.

According to classical colloid theory it is to be expected that the particle size of an emulsion will be increased as a result of the addition of metal ions to the aqueous phase of the emulsion. It can be postulated that the increase in particle size of a lubricant emulsion of the present type in service is due to the take-up of metal ion during the rolling process. Thus aluminium and iron are taken up from the metal being rolled and from the roll surfaces. It is also probable that magnesium will be taken up in significant quantity because of the large proportion of magnesium-containing alloys, which are rolled in most aluminium hot-rolling mills. It is also inevitable that significant quantities of calcium ion will be introduced in the make-up water added to the lubricant daily during service to replace the large quantities of water, which are lost by evaporation on the rolls. Even if so-called deionised water is employed small quantities of calcium ion are introduced. It is not very surprising to find that the deliberate introduction of these ions in the form of soluble salts into the aqueous phase results in the increase in the particle size of the emulsion and in accordance with a first feature of the invention the initial particle size of the emulsion is increased, if necessary, by a controlled addition of a multi-valent metal salt, preferably an aluminium salt, such as aluminium sulphate.

It would be expected from classical colloid theory that the addition of the ion of monovalent metals would have the effect of increasing the particle size, although to a lesser extent than would result from addition of a multi-valent ion. It is now found however, that the addition of cation in the form of an alkali metal soap or under conditions such that an alkali metal soap is formed in situ by reaction with the free fatty acid contained in the oil phase, results in a reduction of the particle size of the oil-in-water lubricant emulsion of the present type. Whilst the addition of soap to the aqueous phase is quite a satisfactory expedient, nevertheless it is preferable to add the free base, which will react with the fatty acid at the surface of the oil phase particles and thus generate the soap at the location of maximum effectiveness. Thus for both reasons of economy and effectiveness the reduction of particle size can most effectively be achieved by the addition of sodium hydroxide or potassium hydroxide.

According to the present invention a method of operating an aluminium rolling mill includes charging the lubricant system of the mill with an oil-in-water emulsion, of which the oil phase includes a hydrocarbon oil base, a substantial proportion of free fatty acid and an amino-soap, initially adjusting, if necessary, the particle size of the particles of the oil phase to an average size within an optimum range of sizes by the addition of multi-valent metallic ion to the aqueous phase or by the addition of an alkali metal soap or material which will generate an alkali metal soap by reaction with free fatty acid, depending on whether increase or decrease of the initial average particle size is required, periodically checking the average particle size of the particles of the oil phase and adding sufficient multi-valent metallic ion or alkali metal soap or material which will generate alkali metal soap by reaction with fatty acid to restore the average particle size to a value within the range of optimum sizes. As already stated, the latter particle-size adjustment is preferably achieved by addition of controlled quantities of an alkali metal hydroxide, preferably sodium hydroxide. Instead of determining the average particle size of the oil phase particles the same information can be inferentially obtained by determination of the content of the metallic ions of the oil phase. Thus by establishing appropriate calibration tables it is possible to calculate the amount of sodium hydroxide to add to a known lubricant emulsion to restore it to a known average particle size when the individual content of sodium and polyvalent metals, particularly calcium, magnesium, iron and aluminium, have been determined. it will be understood that similar results can be obtained by the addition of potassium hydroxide. It will also be understood that sodium and potassium may be introduced into the aqueous medium in the form of their carbonates and bicarbonates or other strongly alkaline salts.

As will be apparent from the foregoing discussion it is preferred to select a lubricant emulsion which gives optimum results at a particle size substantially below the size of troublesome solid particles, which may require removal by filtration.

It has been found in practice that a satisfactory I method of assessing the average particle size of a lubricant emulsion is to estimate the number of particles above a predetermined size in a small volume of the emulsion. For each lubricant composition (oil phase composition) there is an optimum number (N/C), arrived at by dividing the actual number of particles by concentration of oil phase in the emulsion. Very suitably the oil phase particles of a size inexcess of 2 microns are counted. Increase of this number signifies increase in the average particle size. The procedure adopted for determination of the number (N) is to disperse 25 microlitres of emulsion in 250 ml of standard electrolyte and then to count the number of oil droplets above 2p. in size in 0.05 ml of dispersion. C is the concentration by volume of the organic component in the emulsion.

in one series of experiments the lubricant employed in the lubrication system of a hot-rolling mill was an aqueous emulsion containing about 6 percent of an oil phase, which comprised a kerosinic hydrocarbon base oil, containing about 12 percent oleic acid and percent triethanolamine, which reacts in part with oleic acid to form an amine soap emulsifier for the oil phase. The oil phase may also include an extreme pressure lubricant, such as tricresyl phosphate, and a coupling agent, such as diethylene glycol, to help solubility of the additives. However, the particle size of the emulsion is primarily dependent on the concentration of oleic acid (or other fatty acid) and triethanolamine (or other soap-forming amino-base) in the oil phase and the amounts of monovalent and multivalent cations. In the tests in question it was already known from past experience at which number (N/C) the most satisfactory rolling results would be achieved. On initial preparation it was foundthat the NIC was too small and in consequence aluminium sulphate was added in small amounts until the predetermined optimum number of about 700 900 was achieved. During subsequent operation small samples of lubricant were taken at intervals from the system and the metallic ion content of each of the abovementioned metals in the stable oil-inwater emulsion was measured. An appropriate amount of sodium hydroxide was then added to the lubricant system to restore the balance of monovalent metal ion to multivalent metal ion appropriate to the desired particle size.

The present invention provides a method of prolonging the service life of a charge of oil-in-water emulsion lubricant in an aluminium mill over a very long period and thus leads to significant economies in operation.

In further tests the oleic acid content of the oil phase was increased and also the content of tricresyl phosphate, whilst the ethanolamine content was held in the range of 2 4 percent. The levels of oleic acid and tricresyl phosphate were raised from about 13 percent and 2 percent respectively to about 15 percent and 2.5 percent respectively. Further increase of oleic acid to 17 percent can be achieved without difficulty. At the same time corresponding additional amounts of triethanolamine were added. This addition was found to result in an emulsion which gave good rolling results at a significantly lower value of MC (about 200 400) than before. The addition of sodium hydroxide at regular intervals permitted this small particle size also to be maintained over a prolonged period. It is thus now found possible to operate the lubrication system with efficient filtration to remove entrained solid particles. Previously it was found that if tight filtration was employed to remove solids, the loss of oil in the filters was very high. Thus the process of the invention, when employed in conjunction with tight filtration, permits the use of a clean fully-filtered lubricant, thus reducing the amounts of undesirable solid detritus, which is deposited on the aluminium during deformation in the mill.

It is found preferable in the operation of the present invention to make additions of alkali metal material during periods when the mill is shut down to avoid foaming. Additions of multivalent metallic ions for increase of oil droplet size, on the other hand, are preferably made while the mill is in operation to avoid as far as possible the fonnation of extra large droplets, which would be removed by filtration.

All parts and percentages herein are by weight except where stated.

I claim:

1. A method of operating an aluminium rolling mill including charging the lubricant system of the mill with an oil-in-water emulsion, of which the oil phase includes a hydrocarbon oil base, a substantial proportion of a free fatty acid and an amino-soap, initially adjusting, if necessary, the average particle size of the oil phase to an average size within a preselected range of sizes by the addition of multivalent metallic ion to the aqueous phase, or by the addition to the aqueous phase of a hydroxide or strongly alkaline salt of an alkali metal to generate an alkali metal soap by reaction with some of the free fatty acid of the oil phase, depending on whether increase or decrease of the initial average particle size is required, periodically checking the average size of the particles of the oil phase and adding sufacted by the addition of an alkali metal hydroxide.

3. A method according to claim 1 in which the oil phase contains 13-17% fatty acid and 2-2.5 percent tricresyl phosphate and 24 percent triethanolamine reacted with an equivalent proportion of the said fatty acid. 

2. A method according to claim 1 in which the effect of accumulated multivalent metallic ion is counteracted by the addition of an alkali metal hydroxide.
 3. A method accorDing to claim 1 in which the oil phase contains 13-17% fatty acid and 2-2.5 percent tricresyl phosphate and 2-4 percent triethanolamine reacted with an equivalent proportion of the said fatty acid. 